1. Field of the Invention
The present invention relates to a rotation angle sensor which detects a rotational position of a rotating conductor. The invention is based on the principle that the inductance between a conductor attached to a rotating shaft of a rotary member and a coil conductor attached to a stator facing the former conductor changes according to positional relation between both conductors.
Further, the present invention relates to a motor-driven airflow control device which electrically controls an area of opening of an air intake passage of an internal combustion engine by use of a motor-driven throttle valve, the apparatus including the above-mentioned rotation angle sensor in order to detect a rotational angle of the throttle valve.
2. Description of the Related Art
Examples of a so-called non-contact rotation angle sensor, which detects a position or rotational angle of a rotary member through inductance variation, include an apparatus disclosed in JP-A-2003-254782.
This rotation angle sensor includes a magnetic disc and a conductor disc. The magnetic disc and conductor disc each have a slit in a radial direction and intersect with each other at the slits, one of the discs being fixed and the other attached to a rotating shaft, wherein an exposure area of the magnetic disc and the conductor disc viewed from one side of the shaft direction is changed with the rotation to vary the inductance of a coil disposed in proximity thereto, thereby detecting an angular position of the rotating shaft through inductance variation.
Further, the use of this kind of rotation angle sensor as a rotation angle sensor for a motor-driven throttle valve is proposed U.S. Pat. No. 6,886,800.